1. Field of the Invention
The present invention relates generally to a communication interface circuit for transmitting and receiving data, and more particularly to a data synchronization circuit for transferring data between different clocks and to a communication interface circuit including the same.
2. Description of the Related Art
For example, in a communication interface for controlling a data communication between a personal computer and a device such as its peripheral device (for example, a hard disk drive, or the like) or the like, when speeds of a reception side clock and a transmission side clock are different, it becomes necessary to synchronize data between the different clocks. In particular, in a communication interface circuit in which line data to be transmitted at a predetermined clock speed in a communication line are required to convert into internal bus data to be transferred at another clock speed (or its inverse conversion), it is necessary to synchronize the bus data between the different clocks in the interior.
For synchronizing data between the different clocks and transferring the data between circuit blocks operating in clocks differing from each other, a method for using a buffer memory and a method for performing hand-shaking are known. In the method for using the buffer memory, in order to absorb a clock difference between the blocks, the data from the circuit block on a transmission side have once been accumulated in the buffer memory, and the data are output to the circuit block on a reception side in synchronism with the clock of the circuit block on the reception side. In the method for performing hand-shaking, a determination of a communication method, a protocol or the like has in advance been made between the circuit block on the transmission side and the circuit block on the reception side prior to the transmission and reception of the data, and the data is transmitted and received according to the determination.
However, in the method for using the buffer memory, a space for the buffer memory (and a buffer memory test circuit or the like) is required in the interior of the communication interface circuit, and this leads to an obstacle to a downsizing of the communication interface circuit, in its turn a device housing the circuit. Furthermore, a control signal between the circuit blocks is also required, and this makes the control complicated. Furthermore, in the method for performing the hand-shaking also, a control signal and a control circuit therefor are required. This leads to an obstacle to the downsizing of the communication interface circuit, and this makes its configuration complicated. Furthermore, when performing the hand-shaking, a communication speed is relatively late and it is not suitable for a high-speed transfer.